Apparatus for drawing elongated metal objects



May 20, 1952 w. E. KERR APPARATUS FOR DRAWING ELONGATED METAL QBJECTSFiled April 28, 1948 3 Sheets-Sheet l INVENTOR. Wallace E. KP

QM NW WI v% Wm W. E. KERR May 20, 1952 APPARATUS FOR DRAWING ELONGATEDMETAL OBJECTS Filed April 28, 1948 5 Sheets-Sheet 2 l I IN V EN TOR.lVa/lac e E. Kerr.

May 20, 1952 w. E. KERR APPARATUS FOR DRAWING ELONGATED METAL OBJECTSFiled April 2a, 1948 3 Sheets-Sheet 3 INVENTOR lVa/Iace f. KPrr.

Patented May 20, 1952 UNITED STATJ'E'TS PATENT.

APPARATUS FDR'DRAWING EEONGATED METAL OBJECTS Walla-cell. :Kerr,Youngstown, Ohio,

AppIicatibn-ApriFZS, 1948;."S'eriali Noe-23384 8:Claims.. (CLZO'EV- ZThis invention-relates to=-the meta1- drawing art and more particularl yto improved' 'methods apparatus for-drawing finite l'engths-ofmetaiohjectsthrough a die in such manner that. sub-* stantiai ly all scraploss is eliminated and" in such manner" thatpreliminarypreparation ofthe blanks "to be drawn by pointing is obviated; While the inventionto'be disclosed herein has some 'applic'zal-loil'ity in the field of"bar" drawing its greater and more important usefulness-is in tubedrawing and greater emphasis willhccnrd-ihgiy be placed" herein! on thelast mentioned use of the method and apparatus;-

I-t" has" heretofore-"been commonly proposed, in the metal drawingart,to provide pushing: grips inassociation with the drawing-die to extrudethe leading ends of bl'ar-rks of uniform cross-sew tionai shape anddimension throughout-their length through the drawing die sufficiently--toenable them to be-grippedwby thedraw carriage; the outward movement"of whichcompletes the drawing operation. It one of the objects ofthe-present inventionto-=providea novel and improved combination,imam-assembly of the nature indicated;- "of" pushing anti-pulling g-r-ipbits and mounting means therefor-whereby the indicated operation may becarried: outwith: greater facility and in a moredependable man-- ner.-Further, the 'novel combination of the grip hits while providinganentirely"practicablemachine yetnevertheless operativ'eto I draw theentire length of uniformly-crosssection blanks in-"a; dependabl'emannerto provide a" finishedproduct-usable along its entire-length;thuseii'm mating any ne'e'd for cropping.

Another primary object of "the invention is: the provision of improvedmethods and apparatus. for drawingthe entire-longitudinal extent'of'uniformly cross-sectioned tuloeblanks in suchmannerthatthe finishedproduct-is: of uniform: qualitythroughout its length, and free of gripmarks;- -The process and apparatusofthis-in vention isequall'y'applicable in operations whereinn-the thicknessof the side wa ll or:thetuhe is reduced; or-in mere sinking operations:

more specific-- object of the invention is the provision in tube drawingapparatus of the character capablef drawingthe entire lengthoi a"uniformly cross-section blank ofan improved drivingarrangement for thepulling" grip--bits whereby the" initiationof the drawing operationisiaeilitated and-whereby static friction which may appear .betweenthetube -and die is more readiiy'overcome; 7

Yet anotherobject of-the-inventionis-the-pro 2 vision: intuberdrawingapparatustofi the :Lpush"- pointing typeofian-improvedkmandret hick is: operative during the ext-rudingonpush-pointing phase: of a complete cycle to be: positioned 'im movingbutoperative location withinnthe; die:

which has 1a:v furthennrelativeLymovable portion positionedwithimthe:tube blank opposite the: pushing grips." to prevent: collapsing:ofitherblank bythese A still furthers-object of th invention. isatheprovision in: a; tube "drawing: systemzrofwithe kind operative to reducetheiside' .walli thickness iofi' a tube blank-1' throughout itsentirev'long-itudinala extent; of an: improved plug: :nrandrelz; an; innproved 'operatingszlme'chanismi fox'r'suchz mandrel; and Of I'IIIDIOVBIimethods forioperatingaand'con a trolling the: plug mandrel.

other specific obje'cts of the invention: are: the provision: of amimprovedgmethod fior." gripping: an: extruded" endt-of at: tubebla'nkifoncompletiom of: a tubedrawingoperation and ofpracticali apparatus forcarrymgiout suchmethod;

Thesrabove; and; other :ol'ajeotss'and advantages; ofrtherinvention:wilirbenome apparent :upontcomsiderationi'of'ithe: followingdetailedispecificationz and; the. accompanyingsadrawings wherein.therei's. disclosed'iageertamz preferred: embodiment: of thezinven'tionzIn the drawing:

Figures: 1; and-2' are sehematicarviewsr in: plan, of tube: drawing?app'aratusxconstnucteoi in;;a;c:- cordance withvthe principles; 0tinvention; the viewsshowin'gs' the relativetmositionszofzthe parts attww separate stages during the? draw ing cyc'ler,

Figure; Ia isxa fragmentary longitudinat sem tion of certainofi' theparts of the 'assemblyrof Figures 1' and: 21when :the;partsware-relativeliy positioned as, shownin'iiEigure 1.;

Figure 2a @is a viewsimilar-to-- Figure 10, but showing theparts'a'sfthey appearwherr the ma.- chineeistin the conditiomshown:in -Figure2 Figures 3: and 4 are generally similar: to -Figures 1 'and12 'butshow: -the relative positions of the parts: at thefthird' and fourthstage; respectively;of a 'c'omplete draiwmg cycle;

Figures 322:- and. 4a are enlarged fragmentary sections through certainof th parts of the-machine-as they are'rel'ativei'y positioned in-Fig=-'- ures 3- and4, respectively;-

Figure 5 is a view-similar to=Figure-1 but show-- ing' the parts in 1the last stage of the cycle" of operationa Figure fia' isv afragmentarylongitudinal see tion through certaimof the partsor -Fig; *5; Y

Figure 6 is a transverse section taken along the line 6-6 of Figure 5;and

Figure 7 is a transverse section through the drawing mandrel, the viewbeing taken alon the line 1-4 of Figure 2a.

The illustrated apparatus of the invention comprises a draw carriage lmounting a grip block H and slidably supported on suitable ways |2 formovement toward and away from a die stand I3. While any suitable meansmay be employed to move the carriage |0 I preferably utilize a pair ofdouble-acting hydraulic cylinders l4, the piston rods |5 of which extendoutwardly to engage the carriage In to move the same away from andtoward the die stand l3. Hydraulic fluid under pressure is arranged tobe delivered to the rear ends of the cylinders |4 through conduits l6 tomove the carriage |0 outwardly of the die while conduits l! are providedto admit hydraulic fluid under pressure to the forward end of thecylinders M to retract the carriage |0. Recessed in the die stand I3 isa drawing die l8.

Positioned rearwardly of the die stand l3 and intermediate the cylindersI4 is a push-pointing mechanism comprising a grip block 20 and a pair ofrigidly interconnected cylinders 2| receivable over rams 22 which arefixed on a base 23 bearing fixed relation to the die stand l3 and theways l2. It should also be understood that the cylinders M are alsofixed on the base 23. The push-pointing mechanism 20-22 and all itsappurtenances, many of which are not shown, may be of the kind fullydisclosed and claimed in my co-pending application Ser. No. 490,060,filed June 8, 1943, and entitled Method and Apparatus for Drawing Tubes.As shown herein the grip block 20 slidably mounts a pair of serrated andwedgeshaped grip bits 24 and, as more fully explained in said co-pendingapplication, the push-pointing mechanism includes means, not shownherein, for first closing the grip bits 24 onto the stock beforehydraulic fluid pressure is admitted to the rams 22 to move the gripblock 20 forwardly toward the die stand l3 and with means operative atthe completion of a working stroke to open the grip bits 24 and toreturn the grip block back to its initial starting position. Hydraulicfluid pressure is admitted to the rams 22 through the conduits 25.

Slidably mounted in a wedge-shaped window formed in the grip block H ofthe carriage I0 is a pair of smooth faced wedge-shaped grip bits 26which are contoured on their faces in the manner shown in Figure 6 topresent four line contacts with a round bar or tubular member positionedbetween them. The absence of serrations or knurling on the grippingfaces of the bits 26, however, requires the application of veryextensive forces tending to move the grip bits toward each other toclamp a tube with sufiicient rigidity to draw the same through the dieand to accomplish the application of such heavy forces. I positionanti-friction rollers 21 intermediate the inclined outer surfaces of thegrip bits 26 and the adjacent inclined side walls of the wedge-shapedopening in the grip block The grip bits 26 are, in actual practice,mounted in the grip block II in the manner more fully disclosed andclaimed in my co-pending application Ser. No. 740,133, filed April 8,1947, and entitled Metal Drawing Apparatus.

As shown more clearly in said co-pending application Ser. No. 740,133the grip bits are guided for movement parallel with the respectiveinclined side walls of the opening in the block and in the apparatusdisclosed herein means comprising a lever 28 is employed to move thegrip bits 26 longitudinally to close and open the same with respect towork clamped therebetween. As shown more clearly in Figures 1a and 2athe enlarged ends of the bits 26 are pivotally connected to a slidableyoke 29 which in turn is arranged to be shifted back and forth bypivotal movement of the lever 28 about its pivotal anchorage l9.

The frame of carriage I0 is formed with a longitudinally extending bore30 in which is slidably received a sleeve 3| having a slit end 32adapted to be positioned between the grips 26 a shown in Figures 1a, 2aand 6. The longitudinally extending slots in the end 32 of the sleeve 3|divides this end into four equal circumferential segments and is shownmore clearly in Figure 6; each of the segments is arranged to have atleast line contact with the gripping face of the grips 26. For a purposeto be later described the end 32 of the sleeve 3| is retractible fromthe position intermediate the grips 26 and to provide for such,manipulation of the sleeve 3| I provide a lever 33 which is pivoted tothe carriage H1 at 34. Slidably received in the sleeve 3| is an arbor 35which is slidable into and out of position between the grip bits 26. Foradvancing and retracting the arbor 35 I provide a lever 36. It should beunderstood that the levers 28, 33 and 36 are included herein tofacilitate understanding of the principles of the invention, it beingunderstood that in actual practice more suitable power operatedmeans, ashydraulic cylinders, for example, may be employed to actuate the gripbits 26, the sleeve 3| and the arbor 35. This is particularly true asregards the arbor 35 since, as will appear later, the arbor in itsforward position in the grip bits 26 may be employed to assist in theretraction of the drawing mandrel when shifting from pushing operationto full drawing operation.

I provide a drawing mandrel of novel and improved construction comprisedof a rod 31 mounting an elongated plug 38 having the shape and dimensionrequired to form the proper internal opening through the tube to bedrawn. While the plug 38 may be integral with the rod 31 it is usuallymade removable from the rod by means of a screw threaded connection, notshown. Rigidly secured to the plug 38 is a tag 39 which may be ofslightly smaller cross-sectional area than the opening through the tubeto be drawn so that it may readily pass through the tube blank and theopening in the die l8 for engagement by the grip bits 26 or by thesleeve 32 at the start of a drawing operation. The outer end portion ofthe plug 38 is preferably formed of a separable sleeve 40 constructed ofsintered tungsten carbide or other material having superior abrasionresistant characteristics. As will appear later the block portionrepresented by the section 40 will be subjected to the greatest wear andit is accordingly desirable that material of the indicated nature beemployedfor this section. The portion 46 may be of cylindrical form andmay be secured in position by a tapered stud bolt, not shown, integralwith the tag 39 and screwed into the principal portion 38 of themandrel.

Secured on the rod 31 is a collar 4| and interposed between the collar4| and the plug 36 is a sleeve 42 and a coil spring 43 which normallybiases the sleeve 42 into engagement with the plug 38. Sleeve 42 is, ofcourse, slidably fitted on the shank 38 free to slide in the tube blankfor a purpose to be hereinafter described.

Monaco- Therodt'l of the. drawing mandrelisconnected by means. of auniversal jointv 44 with a forward end of a piston rod 45 which in turnextends through an. anchor block Atwh-ich extends upwardly. from thebase 23. A collar 41' is secured in fixed-position on the rod 45 and theblock 46 provided with a gate 41 whichwhen closed is. operative toprevent the passing through the. anchor 4'6. of. the. collar 4.1, in adirection towardthe die I8; Rod 45 is connected to a piston in acylinder 48' which is slidable bodily insuite able ways 49 mounted onthe base 23. and fluid pressure. is arranged to. be admitted to the rearend of: cylinder 48; through conduitxflq. to. ad- Vance the drawingmandrel, and to the. forward end of cylinder .48 through. conduit 51 toretract themandrel. It should be kept in. mind, at this point;- thatsuch actuation of the drawing mandrel'. is: limited in extent by thelength of stroke orthe. cylinder 48. Rigidly connected-with. the

outer housingof. the cylinder 48- is a. rod 52 connected with the pistonin double-acting cylinder 5.3.which is also bodily slidable in the. ways49. Fluid pressure is admitted tow the rear end. of cylinder 53 throughconduit 54'to. move the cylinder 48 toward the die i8 and conduit 55' isprovided to conduct fluid to the forward end of cylinder 53 to retractthe cylinder 48. Rigidly connected. with the outer housing of thecylinder. 5.3"isa rod 56 connected with the piston in a double-actingcylinder 57 which is mounted in fixed relation on the base 23. A conduit58 admits fluid under pressure to the. rear end of cylinder 51 While a.conduit 59 admits. fluid. to the forwardend, of cylinder 51.

To simplify the disclosure herein the various interlocking andsequentially operative electrical and hydraulic control circuitsnormally utilized for. the, actuation and control of. the variouscomponent parts of, the system including the grip bits 26,,the. arborand the. cylinders I l, 2|, 48, 53, and 51 have been omitted and it isbelieved that the operation of the system from the following,fulldescription of a, complete cycle of operation will be readilyunderstood.

At the start of a cycle of operation the parts are relatively positionedas shown in Figures 5 and, 50.. wherein the full retraction of bothcylinders 48. and 53 frees the drawing mandrel entirely from the.pushing assembly even though the latter is also fully retracted and inthis position the mandrel may be readily tilted upwardly about the joint44. to enable a tube. blank to be slid over the outer free end of themandrel. The

mandrelis now re-aligned with the axis of the die andfluid is admittedto cylinder 48 through conduit 50 and through conduit 54 to cylinder'53to advance the tube blank (designated by referencenumeral- 69) intoabutting relation with the die [8. and to advance the working part ofthe mandrel through the die, all as shown. in Figure 1a of the drawing.Gate 41 is open. At; this time the splitsleeve 32 is positioned betweenthe gri bits 25 and after the carriage I0 is returned sufficiently toreceive a substantial length of the projection 39 01. the mandrel in thesleeve 32 the lever 28.is operated to close the grip bits 25 onto thesplit sleeve 32 which in turn moves into tight clamping engagement withthe projection 39. Fluid pressure is now admitted tothe conduits 25 andi6 and immediately the pushing grip bits 24 closeontothe blank 60 afterwhich the grip block 20," begins tomove toward. the die, all asexplained in the above, mentioned co-pending application Ser: No,. 490',06,0 and simultaneously therewithi the carriage "i0 will be movedoutwardly to pull the. mandrel: fur-therthroughi the dieandl' initiatethe drawing of the blank through the. die..- It should be observed; thatdue to. the-reduction. in the side wallthickness of theablank the linearspeed of the blank as it leaves, the die.wi1l.. be greater than the.linear speed of the blanlsas it. enters the die and to prevent; sliding:of the mandrel in the blank either at or immediately following the dieso as to reduce frictionalilosses. as: much as; possible, I. proposetoproportion-the, flow ofv hydraulic fluid to the cylinders M and. 2|-in such manner as to compensate forthis speed variation. Such regulationmay be readily accomplishedthrough the use of variabledis: placementhydraulic fluid pumps or through theuse. of flow control valves, as iswell-understood inthe hydraulics art. Sincethe drawing mandrel movesalong with the drawn portion-of the tube as distinguishedrfroman undrawnportion.

. of the tube,it will be obvious that themandrel shown in. Figures 2and- 2a. At this time the flow of fluid to the conduits l8 and 2511sdiscontinuedabut if the tube has notbeen. extruded is'uie ficiently. tobe clamped by the bits '26 the gri=p block 20 will be backed 01? andboth cylinders l4 and 2!. will be again actuated in a forward directiontoefiect further extrusion and drawing: ofv the tube. Uponsufiicient'tube.being'extruded the flow of fluid to conduit I6 isdiscontinued tointerrupt outward movement of the carriage-10. The-grips.25- will now be opened by manipulation of the lever 28 and the sleeve 32isv retraoted by manipulation of the lever 33. During theinitialcombined extrusion and-drawing operation theforward movement. of thedrawing mandrel was allowed by movement of the piston in the-cylinder511, the cylinders 53v and 48. sliding bodily along the ways d9; Afteropening the bits. 26 fluid is admitted to: cylinder 5'11 throughconduit-J 59 and. to cylinder .53. through conduit- 55 to retract themandrel andv anchor rod liito position the collar 41" immediatelybehind; the gate A7: which is then closed. During such. retraction.the,- push-pointing mechanism which includes; the; grips 2.4-. may beutilized" tonclampand. hold the blankfitl. stationary. The dimensionsof'the parts. are such that when the-collar M2 is: restrained-1 againstoutward movement by the. gate. ,41- the; wear-resistant portion. 49 ofthe drawing;-.man; duel. is positioned. in. operative relation: inthe;vdie l8, as shown inFiguresBq and 4a.

Upon the mandrel portion Ali-beingpositioned and lockedin the diathe.grips Edwill closeouts the tube; with the arbor 35 positioned inside,the

tube and fluid is 'now admitted to the cond its:

At the same-time thetubemay beejectedgirem; between the. grips. 263.and.from the-iree-end t.

the arbor 35" by" operatinglever 33 to slide the" 7 sleeve 32 into thespace between bits 26 formerly occupied by the outer end of the tube.

The desirability for the use of the sleeve 32 arises primarily from thedesirability of making the block ll, grips 26 and associated rollerraces of reasonable length, for compactness, and since the wedge anglemust be quite small to insure a heavy grip closing force. The range ofmovement of the bits 26 in a direction toward or away from each other istherefore necessarily quite limited and ordinarily it would not bepossible for the same set of grip bits to adequately grasp both the tag39 and the drawn tube which is formed on the working portion of themandrel 38, 40. However, use of the sleeve 3|, 32 may be dispensed withif the tube product has very light gauge side walls and if the diameterof the tag 39 is only slightly smaller than the diameter of the workingportion of the drawing mandrel.

As clearly shown in Figures 3a and 4a, the outer end of the tag 33 isprovided with a centrally disposed conical indentation which iscomplementary to the conical free end of the arbor 35. Thus when it isdesired to retract tag 39 from the grip bits 26, i. e., when the mandrelis retracted to position the portion 40 in the die I8, the arbor 35 maybe advanced longitudinally by operation of the lever 36, or other meansemployed, to assist in retracting the mandrel and the interlockinginterconnection between the free end of the arbor 35 and the tag 39 willguide the arbor in the performance of this function. Further, thisinterconnection will guide the entrance of the arbor into the end of thetube as evident from a comparison of Figures 2a and 3a of the drawingwhich illustrate successive steps in the cycle of operation of theapparatus. It should be observed, however, that the force exerted on themandrel through the arbor 35 is merely supplementary to the principalmandrelretraction force exerted by the double-acting cylinders 53 and51. The guiding of the arbor 35 into the end of the tube inherentlyresults in the axial alignment of the grip bits 26 with the tube 60 sothat any possibility of the end of the grip bits 26 colliding with theend of the tube is avoided. This feature is useful since the availableclearance for entering the grip bits 26 over the tube is small.

It can be readily shown that the force required to extrude a tube blankthrough an annular die opening is much greater than is the forcerequired to pull the tube blank through the same die opening.Consequently, even through the initial extrusion of the tube blank inthe present invention is materially aided by a heavy pull on themandrel, the grips 24 must yet exert a very heavy force on the tubesince in any case the beneficial force which can be applied to themandrel in pulling direction can never exceed the axial frictional forcebetween the mandrel and the tube blank. If smooth-faced pushing gripswere employed they would have to be of very large size and theirmounting block would have to be of such weight and dimension as to beimpractical. Therefore, practical considerations do not permit the useof smooth-faced grip bits in the push-pointing mechanism and accordinglysuch grip bits are provided with serrations. These serrations, however,are sufficiently fine so as not to mark the stock to an extent whichcannot be removed in the single pass through the drawing die. Theinvention, therefore, provides an entirely practical method andapparatus whereby elongated metal objects, both bars and tubes, may

8 be readily reduced and drawn throughout their entire axial length andfinished free of any grip marks or other deformation requiring scrappingof any portions of their lengths.

The above specifically described embodiment of my invention should beconsidered as illustrative only as obviously many changes may be madetherein without departing from the spirit or scope of the invention.Reference should therefore be had to the appended claims in determiningthe scope of the invention.

I claim:

1. Apparatus for drawing tubes comprising in combination a drawing die,a push-pointing device positioned ahead of said die and having means togrip the outer surface of a length of stock to extrude the same throughsaid die, a draw carriage having gripping means positioned beyond saiddie, a mandrel having an elongated draw plug adjacent an end portionthereof and being reduced in diameter at said end portion, said grippingmeans on said carriage being operative to engage said reduced endportion of said mandrel and said extruded end portion of said stocklength in succession, means to retract and mandrel, and means to anchorsaid mandrel in retracted position.

2. Tube drawing apparatus comprising in combination a drawing die, apush-pointing device die, a push-pointing device positioned ahead ofsaid die and having means to grip the outer surface of a stock length toextrude an end portion of the same through said die, a draw carriagehaving gripping means positioned beyond said die, a drawing mandrelhaving an elongated sized portion adjacent an end portion thereof, saidgripping means of said carriage being operative to engage said endportion to move said mandrel in said die simultaneously with theextrusion of said stock length by said push-pointing means, means toretract said mandrel, and means to anchor the same in retractedposition, said gripping means on said carriage being also operative toengage the freestanding extruded end portion of said stock length.

3. A mandrel for tube drawing apparatus comprising in combination ashank, an elongated drawing plug secured to one end of said shank, a tagrigidly secured to and extending outwardly of the free end of said plug,a collar on said shank, a sleeve slidably mounted on said shankintermediate said collar and plug, and a coil spring mounted on saidshank intermediate said collar and sleeve to normally maintain thelatter in abutting relation with said plug.

4. A tube drawing apparatus having a drawing die, a push-pointer, a drawcarriage, an elongated-plug type of mandrel having a tag projectingoutwardly therefrom for gripping engagement by the draw carriage, meansto retract said mandrel to a predetermined position relative to said dieafter movement of said mandrel through said die by engagement of saidtag by said draw carriage, and releasable means to anchor said mandrelin said predetermined position.

5. Apparatus according to claim 4 further including a pair of cylindersmounted in tandem for retracting said mandrel to said pred t minedposition, one of said cylinders being fixed with respect to said die andthe other of said cyhnders being intermediate between the piston rod ofsaid one of said cylinders and said 9 mandrel .and being slidablymounted for movement toward and away from said die.

6. Apparatus according to claim 5 further including a third slidablymounted cylinder interconnected between the piston rod of said secondmentioned cylinder and said mandrel, the arrangement being such thatactuation of said second and third cylinders in a forward direction isnormally operative to move said mandrel forwardly through said die intoposition for engagement by said draw carriage while actuation of saidfirst and second mentioned cylinders in a reverse direction is operativeto retract said mandrel to said predetermined position while said thirdcylinder is fully actuated in a forward direction.

7. Tube drawing apparatus comprising an elongated drawing plug, a tagrigidly secured to and extending outwardly of one end of said plug andadapted to be engaged by a draw carriage, an anchor rod secured to andextending axially outward of the other end of said drawing plug, meansengaging the rearward extremity of said anchor rod to limit the forwardmovement of said anchor rod and to retract said anchor rod to apredetermined rearward position, and releasable means engaging said rodto retain the same in said predetermined rearward position.

8. Apparatus according to claim 7 further in-' cluding a universal jointin said anchor rod whereby the forward portion of said anchor rod andsaid plug and tag may be tilted upwardly with respect to the axis of therear portion of said anchor rod.

WALLACE E. KERR.

REFERENCES CITED The following references are of record in the file ofthis patent:

UNITED STATES PATENTS Number Name Date 565,726 Rice Aug. 11, 1891894,737 Higgins July 28, 1908 1,132,531 Webster Mar. 16, 1915 1,626,176Atwood Apr. 26, 1927 2,331,953 Andrews Oct. 19, 1943 2,335,939 Hill Dec.'7, 1943 2,351,710 Sanders June 20, 1944 2,428,474 Snively Oct. 7, 1949FOREIGN PATENTS Number Country Date Great Britain June 14, 1945

